Method for the manufacture of tough cast iron



3,065,070 Patented Nov. 20, 1962' 3,065,070 METHOD FOR TIE MANUFACTUREOF TOUGH CAST IRON Kokichi Otani, 64 Hanezawa-cho, Shibuya-ku, Tokyo-to,Japan N Drawing. Filed Feb. 15, 1960, Ser. No. 8,714 Claims. (Cl.75-130) This invention relates to a method for manufacturing tough castiron characterized by combining molten iron in a furnace or molten irontaken from a furnace with a rare earth ore and then inoculating themixture by blending a specific amount of inoculant such as Oa-Si, CaFand Al so as to provide a strong deoxidizing atmosphere to thereby formtough nodular graphite cast iron.

By the term furnace used herein is meant a furnace which produces molteniron, namely electric furnace, reverberatory furnace, melting furnaceand blast furnace, and any one of these furnaces may be used forcarrying out the method according to this invention. By rare earth oreis meant monazite and bastnasite. All of these materials consist of thesame ingredients With only the exception that there is a difference inthe contents of rare earth elements. Monazite is abundantly availablequantitatively as well as being cheap. By strong deoxidizing atmosphereis meant an atmosphere which would be suitable for expelling oxidespresent in the molten iron and which is formed by the action ofinoculants such as calcium silicide (Ca-Si), fluorite (CaF and aluminum(Al). By blending-a specific amount of inoculant is meant blending amixed powder ortablets consisting of a specific blend of inoculants.

In describing the method according to this invention, I shall firstexplain the prior known methods andcor'npare them with this method. Asknown methods there are the following:

(a) Method which employs Mg or Mg alloy as inoculant,

(b) Method which employs Ce and an alloy of the Ce grou as inoculant, MH

(0) Method which employs a combination of Ce and an alloy of the Cegroup and Mg or -Mg alloy asinoculant,

(d) Method which employes a high gradealloy of rare earth elementsrefined from rare earth ores as inoculant.

According to the present invention which differs from these knownmethods, the rare earth ores are. notrefined' but are used as they arein a specific amount.

Rare earth ores contain oxides. which acidify molten iron, and in orderto make them neutral or alkaline, they are subjected to the action of aspecified amount of a deoxidizing agent to effectively form toughnodular graphite cast iron. That is, the rare earth ores are used asthey are without being refined, and for the entailing deoxidation of theoxides contained in them they are inoculated and reacted with asubstantially effective amount of a deoxidizing inoculant. The productsobtained according to this method have a wide range of hardness betweenShore (Hs) 100-30, and as to strength, although there is a differencedepending on hardness, they have a strength of 35 kg./mm. -110 kg./m.m.or two to eight times stronger than conventional cast iron. Furthermore,a distinctive feature of the cast iron produced by this method is thatit possesses an extremely stable hardness that will not deteriorate evenwhen the cast iron is annealed.

According to the present invention, a specific amount of cast iron isinoculated under a strong deoxidizing atmosphere. Any excess ordeficiency of this specific or basic amount will change the cast ironobtained. Thus,

' to maintain this basic amount is a requirement for manuores. Itcontains 45-60% rare earth oxides. Bastnasite contains 65-70% of rareearth oxides.

An example of mo'nazite is given below.

Example of Malaya M nwzite I Percent C602 v 1,320 r Nd' Og p 9.7 'zoa iResidual rare earth oxides 4.147

Rare earth oxides 53.87 ThO 7.15 SiO Balance facturing tough nodulargraphite cast iron. The basic inoculants to be added are Ca-Si, CaF Aland monazite. Of these materials a part of Ca-Si may be substituted byFe-Si and a part of OaF by CaO. Monazite may be entirely substituted bycerium chloride or bastnasite. These substitutions will in no way effectthe deoxidation or the graphite nodulation.

Ca-Si consists of Si Ca 30% and Fe 8%. The more Ca it contains thebetter it is, but those calciumsilicites having a Ca content above thisare difficult to use as they will weather. Monazite (or cerium chlorideor bastnasite) is a representative rare earth ore but contains oxygenand other materials of strong acidity such as SiO and the like in theform of oxides.

It is essential to separate oxygen and such oxides as Si0 as basic slag,and for this purpose a specific amount of a deoxidizing agent isrequired.

If this rare earth ore should be substituted partly or wholly by arefined rare earth of high grade, a small amount of deoxidizingagentwill do. On the one hand the cost of such rare earth is high whichreduces its.

Monazite is produced the most among the rare earth An example ofbastnasite produced in Congo, Africa, has the following analysis:

Percent CeO 33.4 La O 21.75 M1 0 I I 11.07 Residual rare earthoxides0.95

. Rare earth oxides f'67.l7

A Trace P 0 9. 0 Fe O -ii 2.00 F 3.1g Ignition loss 13.20

The higher the grade of rare earth oxides the less the amount ofdeoxidizing agent required, and .vice versa the-lower the grade of rareearth oxides themore the amount of deoxidizing agent required. .The costof monazite is determined by the contents of these rare earth oxides,and those containing approximately 60% rare earth oxides cost about$020-$028. Bastnasite of 50-60% grade is $076-$081 per kg.

In case of refined misch metal, the cost is $8.40per kg. which is 15times higher than monazite in terms of purity. The cost of cerium oxideand cerium fluoride is $196-$230 per kg. which is 10 times higher thanthat of monaz-ite.

To use monazite as an inoculant is suitable from the (CaSi-I-Al +CaZF+Monazite=3 .46-3.78)

The molten iron may be taken from an electric furnace, melting furnaceor reverberatory furnace but it is preferable that the sulphur andphosphorus contents be under 0.020% and under 0.1%, respectively. If thecontents of sulphur and phosphorus should be higher than specified, itwill be necessary to remove them from the furnace. As means oftheir'removal argon and nitrogen gas are fed into the furnace or theremoval may be effected by charging calcium carbide, calcium oxide (CaO)and the like within the limits.

As to the inoculating amount of the inoculants to be added, a goodcompounding ratio is Ca-SizAl:CaF MonaZite=2.5 0.32:0.32:0.320.64

It is more convenient to use the inoculants in the form of tabletsprepared within this compounding ratio.

' When the sulphur and phosphorus contents in the molten iron are withinthe specified limits, the amount of the inoculants to be added Would beas described above, namely molten iron:tablets:100:3.46-3.78, but if thesaid contents should depart from the specified limits, the object canthen be accomplished by increasing the above amount of tablets. If thesulphur and phosphorus contents should be 0.030 and 0.20, respectively,it cannot absolutely be said so but 3.73-3.46X2 would be practicable.

If sulphur and phosphorus are contained within the limits describedabove, it would be economical since a less amount of inoculan ts to beadded would be required.

The following are examples of this invention.

(In the following examples the symbol Hy is an abbreviated symbol ofVickers hardness number, and Hs represents an abbreviated symbol ofShores scleroscope hardness number.)

EXAMPLE 1 Furnace used: Electric furnace. Pigiron used:

- High purity pig iron: 10 kg. (C, 3.59; Si, 0.35; Mn,

0.05; S, 0.015; P, 0.022). Coke pig iron: 10 kg. (C,'4.3; Si, 1.19; Mn,0.15; P,

0.090; S, 0.024). Ferroniokel: 2.2 Kg. (C, 3.3; Si, 0.85; Ni, 22; Cr,

1.19). Melt-down: Me-Mn--l g.; Fe-Cr260 g. Tapping temperature: 1560 C.Casting temperature: 1400 C.

Inoculation:

Charged into the molten metal in the furnace: CaSi,

grams. Laid at the bottom of the pan:

4 Having Shores scleroscope hardness number 60 and Vickers hardnessnumber (by 30 kg. load) 434, this product is suitable for roll material.

EXAMPLE 2 Furnace used: Electric furnace.

Pig iron used:

High purity pig iron: 11 kg. (C, 3.40; Si, 0.37; Mn.

0.08; P, 0.021; S, 0.017). Coke pig iron: 11 kg. (C, 4.3; Si, 1.20; Mn,0.16; P,

0.085; S, 0.025). Melt-down: Fe-Mnl00 g. Tapping temperature: 1510" C.Casting temperature: 1400 C. Inoculation (total 640 g. were mixed andformed into tablets and inoculated in the ladle):

Grams Ca-Si 360 CaF 70 A1 70 Monazite 140 Chemical analysis of theproduct:

0 Si Mn P S N1 Cr 3.78 i 1.40 0.45 i 0.005 0.018 i EXAMPLE 3 Furnaceused: Electric furnace. Pig iron used:

High purity pig iron kg 7.2 Perronickel ..kg 2.5 Fe-Cr g 245 Melt-down:Fe-Mn g.; Fe-Mo-50 g. Tapping temperature: 1530" C. Casting temperature:1450" C. Inoculation (blown in with nitrogen) Grams Ca-Si 250 CaF 30 A130 Monazite 60 Chemical analysis:

ClSilMnP s NiCrlMo 3.56 1.53 I 0.47 0.095 0013 l 5.35 1.92 k 0.32 l

Vickers hardness number (30), 700. Shores scleroscope hardness number(conversion value), 81. Shores scleroscope hardness number (actualvalue), 82.

EXAMPLE 4 Furnace used: Electric furnace. Pig iron used:

Tapping temperature: 1510? C. Casting temperature: 1450 C. Inoculation:

5 6 Chemical analysis: Chemical analysis:

I si Mn P I s I N1 Cr I Mo H O Si Mn P v S N or 3.40 I 1.96 I 0.58 0.057I 0.018 I 2.13 I 0.48 I 0.28 3A6 1.87 0.48 M04 (1016 226 M1 This producthas a Shores scleroscope hardness number EXAMPLE 7 40 Furnace used:Electric furnace EXAMPLE 5 Pig iron used (same as before): Kg. Furnaceused: Reverberatory furnace. High purity pig iron 10 Material usedPercent gg C Si Mn 7 P S Ni Or Mo Feeder head 14.3 2,000 3.17 1. 95 0.350.004 0.021 3.30 1.13 0.29 0.45 0.05 0.05 0.009 0.003 0.47 0.17 0.04Fe-Ni 75 n 3.7 512 3.3 0.61 0.12 0.02

Fe-Ni 70 3. 5 500 3. 21 0. 37 0.11 0.01

Fe-Ni 71 3. 9 413 3. 10 0. 00 0.09 0. 02

Molten metal remaining from a 10.7 1,500 3.3 2.0

previous test. 0.35 0.21

High purity pig iron 65. 0 9, 100 3. 84 0.15

Fe-Cr 156 0.67

Fe-Mo 54 Melt-down: Coke pig iron 10 35 Ferronickel 2 .2 :2" ggMelt-down: Fe-Mn-IOO g.; Fe-Cr-26O g. 20 Tapping temperature: 1530 C.Fesi 15 Casting temperature: 1400 C.

" Inoculation (inoculated in the pan): Grams Tapping temperature: 1480C. 40 (la-s1 u 500 Casting temperature: 1360" C. CaF 2 200 Inoculation:A1 200 Inoculated in the furnace: Ca-Si, 222 kg. Monazlte 400 Inoculatedin the pan: Ch i l l i Ca-Si 222 A1, 47 C Si Mn P 8 Ni Cr CaF 47Monazlte 96 3.63 1. 91 0. 46 0.120 0.016 1. 35 v0. 74 50 Cnemlcalanalysls of the product: Especially fine nodular graphite cast iron wasobtained.

0 s1 Mn P s Ni Cr M0 EXAMPLE 8 Furnace used: Electric furnace 2.79 2.100.76 0.002 0.011 3.00 0.35 0.29 Pi i used; High purity pig iron 10 Cokepig iron 10 EXAMPLE 6 Ferronickel 2.2

Furnace used: Electric furnace gi E (Inoculated the pan) CaF High pur1typlg iron 10 Al 35 Coke pig iron 1O T 'Ferronickel 2.2 Monazlte Mlt-down; F Mn 1()() g F -C 26() g, 5 By maintaining the mixingproportion of the inoculants Tapping temperature; 1510" C, andinoculating a large quantity, good quality nodular Casting temperature:1380 C. graphite cast iron may be obtained. However, althoughInoculation (inoculated in the pan): G a the use of an excessive amountof inoculant will produce Ca-Si 500 good quality products, not only willit not pay from the CaF 140 70 e nomical standpoint but also when alarge quantity A1 140 f inoculant is employed the temperature of the mhe Monazite 280 metal will drop and thereby produce adverse effects. By

The product obtained is of good quality having high ferrite content andbeing tough.

maintaining the mixing proportion of the inoculants and inoculating asmall quantity, nodular graphite will convert to fine eutectic graphitecast iron having a high degree of toughness. Further, by inoculating astill less amount, the effect of the inoculant will diminish, but theresulting product whether in the form of eutectic crystals or flakesstill exhibits the properties of tough graphite cast iron more thanthose products in the same form which have not used such inoculant. (Thescope of this invention refers to a scope in which effects are obtainedby inoculating the specific amount of inoculant.) Nodular graphite castiron of good quality will be obtained if the proportions of Ca-Si, Al,CaP and monazite to be added to a molten metal obtained by melting 22kg. of pig iron in an experimental 30 kg. model Detroit type electricarc furnace are above the proportions given in the following table. Theuse of pig iron of high purity will require a small quantity ofinoculant.

High purity pig iron, percent..... 100 80 60 50 40 20 Charcoal pig orcoke pig iron,

percent 0 20 40 50 60 80 100 In case of proportions above those given inthe above table, for example, when high purity pig iron is 100% and theamount of Ca-Si, Al, CaF and-monazite should be 600 g., 70 g., 70 g.,and 140 g., respectively, nodulation will of course be easier. On theother hand, when coke pig iron is 100% and the amount of Ca-Si, Al, CaFand monazite should be 600 g., 70 g., 70g, and 140 g., respectively,there would be a shortage of 400 g. of Ca-Si and therefore asatisfactory nodular graphite cast iron will not be obtained but a tougheutectic graphite cast iron will be obtained. Further, taking theproportion of pig iron as basis, that is, if 22 kg. of high purity pigiron and coke pig iron are melted in a 40%:60% ratio, a satisfactorynodular graphite will be obtained if the amount of Ca-Si, CaF Al, andmonazite are 600 g., 70 g., 70 g., and 140 g., respectively.

If the amount of Ca-Si should be varied, the respective amount of Al,CaF and monazite should be increased or decreased accordingly. Thisrelation is shown in the following table.

These proportions were found through experiments. Since a highly refinedpig iron (so-called high purity pig iron which has low sulphur andphosphorus contents) has been refined so as to reduce its sulphur andphosphorus contents, harmful elements such as oxides and hydrides havebeen expelled simultaneously and consequently to use such pig iron willrequire a less amount of deoxidizing agent. Accordingly, it means thatthe quantity of deoxidizing agent required will vary according to thepurity of the pig iron.

I will next explain the mutual relation between the CaF Al, andmonazite. The monazite does not comprise refined rare earth elements butconsists of rare earth oxides and other impurities such as SiO combinedtogether, and among the constituents those effective in the molten metalare the rare earth elements. The monazite will be placed in a statewhere it Will be refined simultaneously in the molten metal. Whatremoves the oxides is the aluminum, and in case of a large amount ofmonazite, it is necessary to increase the amount of aluminum. When highpurity cerium fluoride or cerium oxide m-isch metal is used in place ofmonazite, a small amount of CaF and Al will sufiice but this would notpay from the economical standpoint. Examples are given as follows:

EXAMPLE 9 Furnace used: electric furnace Pig iron used: Kg. High puritypig iron 2l Ferronickel 2.3

Melt-down: Fe-Mn60 g. Tapping temperature: 1570 C. Casting temperature:1460 C. Inoculation:

(inoculated in the molten metal in the furnace: Ca-

Si-350) Charged into the pan: Grams Ca-Si 350 Ffi-Si CaF 50 Al 18 Ce l0EXAMPLE 10 Furnace used: electric furnace Pig iron used: Kg. High puritypig iron 20 Ferronickel 2.1

Tapping temperature: 1580" C. Casting temperature: 1500 C Inoculation(Inoculated in the furnace: Ca-Si--300) Charged into the pan: GramsCa-Si 300 Fe-Si 100 CaF Al 18 Ce 5 To increase the amount of CaF impartsfluidity to the slag and is effective in making the residues which haveaccomplished the deoxidation, namely A1 0 or Slo to fioat and beexpelled.

The use of a large amount of AI will be attended by an exothermicreaction and consequently prevent the temperature of the molten metalfrom dropping (flow temperature is an unfavorable condition).

What I claim is: v A mst qd o ma ufa ur n nodu r g ap cast Iron mpr sint e steps o makin bo 100 pa s by weight of an iron composition having asulphur content of under 0.020% and a phosphorous content of under0.10%, combining with said molten iron about 0.32 to about 0.64 part ofa rare earth ore containing about 45 to 70% rare earth oxides, about 2.5parts calcium silicide, about 0.32part aluminum, and about 0.32 partfluorite.

2. A method as claimed in claim 1 including the prior steps of meltingan iron composition containing more than the desired amount of sulphurand phosphorous, removing from said molten iron in the furnace theexcess sulphur and phosphorous content to yield an iron compositionhaving a sulphur content of under 0.020% and a phosphorous content ofunder 0.10%.

3. A method as claimed in claim 1, said additives being at leastpartially in tablet form containing all four ingredients.

4. A method as claimed in claim 1, said rare earth ore being bastnasite.

5. A method as claimed in claim 1, said rare earth ore being monazite.

References Cited in the file of this patent UNITED STATES PATENTS Cromeu Apr. 18, 1961

1. A METHOD OF MANUFACTURING NODULAR GRAPHITE CAST IRON COMPRISING THESTEPS OF MELTING ABOUT 100 PARTS BY WEIGHT OF AN IRON COMPOSITION HAVINGA SULPHUR CONTENT OF UNDER 0.020% AND A PHOSPHOROUS CONTENT OF UNDER0.10%, COMBINING WITH SAID MOLTEN IRON ABOUT 0.32 TO ABOUT 0.64 PART OFA RARE EARTH ORE CONTAINING ABOUT 45 TO 70% RARE EARTH OXIDES, ABOUT 2.5PARTS CALCIUM SILICIDE, ABOUT 0.32 PART ALUMINUM, AND ABOUT 0.32 PARTFLUORITE.